Great Purple Hairstreak

Most butterfly and moth species, like this great purple hairstreak, depend upon one species of plant to lay their eggs that will later successfully grow into caterpillars.

Sparse rains brought reduced plant growth and insect hatching this summer. What effect has this had on the San Pedro Riparian National Conservation Area and elsewhere? Why should we care?

Insects and some reptiles hatch and reproduce when there is rain and good source of plants for food. Here are some examples:

Grasshopper species lay eggs in the soil that typically stay in the soil through the winter. The success (quantity of rain) of the monsoon effects hatching and numbers. Winter precipitation can play a role as well. And although many humans could do without grasshoppers, these insects are essential to the system.

Most butterfly and moth species depend upon one species of plant to lay their eggs that will later successfully grow into caterpillars. The caterpillars are dependent upon that same plant for nourishment. Even some bats need certain plants.

The local spadefoot toad depends upon the rain for its entire life cycle, emerging from dry mud-caked underground “beds” when the first rains hit in late June or early July. Their entire reproduction cycle relies upon puddles of water over about eight days and then they burrow back underground when the moisture level retreats and cooler temperatures arrive. They can survive for over a year in their burrow during drought conditions, but our drought patterns now often extend beyond one season.

The next layers of animals, herbivores and predator species, rely on insects and plants to be in good supply to support their own life cycles and reproductive success. We start to see skinny snakes, emaciated raptors, fewer quail and other birds, fewer bats, fewer rodents.

Not all plants are immediately vulnerable. Those with deep roots still find moisture. That is why you will see mesquite beans, manzanita berries and acorns still plentiful. Thus, deer and javelina along with their predators are reported to be healthy.

It isn’t just the paltry 3.6 inches this past summer that challenges the natural world. The monsoon has started later and ended earlier for several years now. While the frequency of rain historically has been every two to four days, the last five years or so rains have occured every seven to 10 days. The result is a steady pattern of less water delivered to the system.

When the cycle of infrequent and diminished precipitation continues, the tiers of the ecosystem begin to unravel and the balance of populations shifts. While we lose pollinators (butterflies, bees, wasps, beetles, ants) we gain huge numbers of other insects. Often these other insects are destructive, such as beetles that destroy trees. Viruses and fungi that parasitize and destroy both plants and animals appear. Eventually even the deep-rooted plants show signs of distress, leaving their herbivore diners vulnerable to starvation.

We can only hope that the drought this year does not foreshadow the future. Disruption of the natural order by changing rainfall, increased temperatures, and more extreme weather puts habitats like that preserved in the SPRNCA at risk. The world will become a sad, lonely place for humanity without these quiet, natural locations that are so important as a place to rest and recharge. Myself, I cannot imagine not having a grassland or river walk to refresh and reboot my spirit!

Submitted by Mary Ann Ambrose, with credit to Ron Stewart and Ted Mouras. Ambrose is a retired nurse practitioner with extensive education in zoology and ornithology. She is a volunteer for the Friends of the San Pedro River.